Substantial developments have been achieved in the synthesis of chemical vapour deposition (CVD) diamond in recent years, providing engineers and designers with access to a large range of new diamond materials. CVD diamond has a number of outstanding material properties that can enable exceptional performance in applications as diverse as medical diagnostics, water treatment, radiation detection, high power electronics, consumer audio, magnetometry and novel lasers. Often the material is synthesized in planar form; however, non-planar geometries are also possible and enable a number of key applications. This paper reviews the material properties and characteristics of single crystal and polycrystalline CVD diamond, and how these can be utilized, focusing particularly on optics, electronics and electrochemistry. It also summarizes how CVD diamond can be tailored for specific applications, on the basis of the ability to synthesize a consistent and engineered high performance product.

A novel electrochemical approach to the direct detection of hydrogen sulfide (H2S), in aqueous solutions, covering a wide pH range (acid to alkali), is described. In brief, a dual band electrode device is employed, in a hydrodynamic flow cell, where the upstream electrode is used to controllably generate hydroxide ions (OH(-)), which flood the downstream detector electrode and provide the correct pH environment for complete conversion of H2S to the electrochemically detectable, sulfide (HS(-)) ion. All-diamond, coplanar conducting diamond band electrodes, insulated in diamond, were used due to their exceptional stability and robustness when applying extreme potentials, essential attributes for both local OH(-) generation via the reduction of water, and for in situ cleaning of the electrode, post oxidation of sulfide. Using a galvanostatic approach, it was demonstrated the pH locally could be modified by over five pH units, depending on the initial pH of the mobile phase and the applied current. Electrochemical detection limits of 13.6 ppb sulfide were achieved using flow injection amperometry. This approach which offers local control of the pH of the detector electrode in a solution, which is far from ideal for optimized detection of the analyte of interest, enhances the capabilities of online electrochemical detection systems.

Highly doped, boron doped diamond (BDD) is an electrode material with great potential, but the fabrication of suitable electrodes in a variety of different geometries both at the macro- and microscale, with an insulating material that does not compromise the material properties of the BDD, presents technical challenges. In this Technical Note, a novel solution to this problem is presented, resulting in the fabrication of coplanar macro- and microscale BDD electrodes, insulated by insulating diamond, at the single and multiple, individually addressable level. Using a laser micromachining approach, the required electrode(s) geometry is machined into an insulating diamond substrate, followed by overgrowth of high quality polycrystalline BDD (pBDD) and polishing to reveal approximately nanometer roughness, coplanar all-diamond structures. Electrical contacting is possible using both top and bottom contacts, where the latter are defined using the laser to produce non-diamond-carbon (NDC) in the vicinity of the back side of the BDD. We present the fabrication of individually addressable ring, band, and disk electrodes with minimum, reproducible controlled dimensions of 50 μm (limited only by the laser system employed). The pBDD grown into the insulating diamond recesses is shown to be free from NDC and possesses excellent electrochemical properties, in terms of extended solvent windows, electrochemical reversibility, and capacitance.

Ti–B–N coatings with stoichiometries corresponding to a region of the phase diagram in which a three phase TiB2+TiN+BN composition is predicted, have been deposited by reactive magnetron sputtering. Characterization of the films by x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), glancing angle x-ray diffraction (GAXRD), and extended x-ray absorption fine structure (EXAFS) has been performed to provide information on chemical composition and microstructure. GAXRD and EXAFS have shown the Ti based phases to be dominated by the presence of nanocrystalline TiB2, the grain size of which decreases to an unmeasurably low value with increasing N content. Evidence of TiB2, TiN, and BN bonding is found in the XPS spectra and the inferred phase composition has been found to be in good agreement with that predicted by the phase diagram. From XPS and AES spectra, the BN phase present has been concluded to be of the hexagonal type.

The combination of low absorption and extreme mechanical and thermal properties make diamond a compelling choice for some more extreme far infrared (8-14 mm) window applications. The optical properties of CVD diamond at elevated temperatures are critical to many of these extreme applications. The absorption coefficient of diamond has been assessed on polished diamond samples with a variety of optical characteristics by heating samples up to 550 C and measuring transmission in a grating IR spectrophotometer. High temperature transmission spectra in the range 5000-200 cm --1 (2-50 mm) for CVD diamond are presented. The transmittance at near IR wavelengths %4200 cm --1 (2.5 mm) appears to be only slightly affected by elevated temperatures and the three-and two-phonon regions exhibit the expected temperature dependence. In the far infrared, the transmission drops with a broad peak approximately centred at %1250 cm --1 (8 mm), a behaviour characteristic of all samples tested. The temperature dependency of the absorption coefficient has been deduced by assuming there are no additional scatter losses from the surface and calculating the refractive index at temperature, thus allowing the reflectance at that temperature to be estimated. Direct emissivity and photo-thermal deflection measurements are in agreement with these measurements. An empirical formula for predicting the variation of absorption coefficient at %1000 cm --1 (10 mm) with temperature, is presented.